1. Field of the invention
The present invention relates to tools resistant to a mechanical shock and more particularly to tools likely to be subjected to a shock listed below.
1. Sporting goods such as a tennis racket frame, squash racket, badminton racket for absorbing a shock applied by a ball. PA0 2. Sporting goods for absorbing a shock such as helmet; fencing plastron, fencing face-guard: crotch protecting tool; football shoulder protecting tool; ice hockey mask; ice hockey knee pad and elbow pad; soccer, squash racket, leg guards; ear protecting portion of water polo cap; horse saddle and the like. PA0 3. Helmets for protecting head from accidental shock in riding car or bicycle, in construction work, and infant's play. PA0 4. Bicycle frame, bicycle handle, canoe and the like for absorbing a shock and preventing breakage against a shock. PA0 5. Protecting wall, against machine tool, for preventing the transmission of a shock.
2. Description of the related art
Conventionally, goods required to have a shock resistant performance are made of ABS resin, polycarbonate resin, fiber reinforced resin (FRP) formed by reinforcing thermoplastic resin with short fiber or fiber reinforced resin (FRP) formed by reinforcing thermosetting resin generally with chopped strand mat of glass. The chopped strand mat of glass may be replaced by continuous fiber, long fiber or short fiber consisting of glass fiber, carbon fiber, aramid fiber, boron fiber or ultra-high-molecular-weight polyethylene fiber. Unsaturated polyester resin is mainly used as matrix resin.
The following methods are used to manufacture the above fiber reinforced resins formed by reinforcing thermosetting resin with chopped strand mat of glass: a half-hardened prepreg formed by impregnating fiber with resin is cut to an appropriate size and a configuration, and then, cut materials are laminated on each other in a die, then, heated under pressure so as to harden the resin; chopped strand and resin are sprayed up in a die and then hardened; reinforced fibers are laminated on a balloon-shaped die, then, the reinforcing fiber is impregnated with resin and then, hardened.
Comparing the above materials and manufacturing methods, shock resistant tools made of only ABS resin or polycarbonate resin do not have a favorable rigidity because they do not contain a reinforcing material. Compared with long fiber or continuous fiber, fiber reinforced resin (FRP) formed by reinforcing thermoplastic resin with short fiber has also an unfavorable rigidity.
In the case of the fiber reinforced resin (FRP) formed by reinforcing thermosetting resin with chopped strand mat of glass, shock resistant performance of molded goods can be increased by using reinforcing fiber and matrix resin favorable in shock resistant performance and increasing the content percentage of reinforcing fiber. But it is uneasy to increase fiber content and the method for manufacturing the above shock resistant goods has problems.
That is, fiber content percentage can be increased by cutting the prepreg sheets having thermosetting resin impregnated therein to a certain configuration, laminating cut materials on a die, and heating them under pressure. But the molded goods is inferior in shock resistant performance because thermosetting resin is inferior in shock resistant performance. In addition, this method has an unfavorable production cycle and moreover, the manufacturing cost is high.
Further, in spray-up method or bag method, glass fiber and unsaturated polyester are used in combination. These systems have a disadvantage that resin does not penetrate through fine gaps between fibers, and voids are left between filaments. The disadvantage is attributed to the high viscosity of resin. When resin is injected at a high pressure to accelerate the permeation of resin between fibers, fiber are moved and twisted by the flow of resin. Thus, resin cannot be injected at a high pressure. Therefore, fiber cannot be contained at a high percentage in a shock resistant tool. For example, fiber is contained in a helmet commercially available at approximately 30% at most.